Expansion apparatus having resistive medium

ABSTRACT

An apparatus for expanding a portion of a tubular within a wellbore. The expansion assembly first comprises an expander tool. The expander tool is preferably a rotary expander tool which is lowered into the wellbore at the lower end of a working string. In one aspect, the rotary expander tool defines a tubular body having recesses, with each recess containing a compliant roller. The expansion assembly further comprises a chamber having a resistive medium therein. In one arrangement, the medium is a clean oil loaded into the chamber before being run into the wellbore. The fluid chamber is sized and configured to sealingly receive an elongated lower portion of the body of the expander tool. As the body of the expander tool travels into the fluid chamber, it encounters resistance from the fluid loaded therein. The fluid serves as a resistant force to the downward movement of the drill string and the expander tool during the expansion process, thereby preventing any rapid springing of the pipe string above it.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to methods for wellbore completion.More particularly, the invention relates to an apparatus for expanding atubular in a wellbore.

[0003] 2. Description of the Related Art

[0004] Hydrocarbon and other wells are completed by forming a boreholein the earth and then lining the borehole with steel pipe to form awellbore. After a section of wellbore is formed by drilling, joints ofpipe are lowered into the wellbore and temporarily hung therein from thesurface of the well. Using apparatus known in the art, the joints ofpipe, or “casing,” are cemented into the wellbore by circulating cementinto the annular area defined between the outer wall of the casing andthe borehole. The combination of cement and casing strengthens thewellbore and facilitates the isolation of certain areas of the formationbehind the casing for the production of hydrocarbons.

[0005] It is common to employ more than one string of casing in awellbore. In this respect, a first string of casing is set in thewellbore when the well is drilled to a first designated depth. The firststring of casing is hung from the surface, and then cement is circulatedinto the annulus behind the casing. The well is then drilled to a seconddesignated depth, and a second string of casing, sometimes referred toas a “liner,” is run into the well. The second string is set at a depthsuch that the upper portion of the second string of casing overlaps thelower portion of the first string of casing. The second liner string isthen fixed or “hung” off of the existing casing by the use of slipswhich utilize slip members and cones to wedgingly fix the second pipestring in the wellbore. The second pipe string, or liner, is thencemented. This process is typically repeated with additional linerstrings until the well has been drilled to total depth. In this manner,wells are typically formed with two or more strings of casing of an everdecreasing diameter.

[0006] Apparatus and methods are emerging that permit tubulars to beexpanded in situ. The apparatus typically includes expander tools whichare run into the wellbore on a working string. The expander toolsinclude radially expandable members which are urged outward radiallyfrom the body of the expander tool and into contact with a tubulartherearound. The expander tools may be actuated either mechanically, orthey may be fluid powered. In the case of a hydraulic system, fluidpressure is applied to a piston surface located at the back of theexpansion members. As sufficient pressure is generated on the respectivepiston surfaces, the expansion members move radially outward from theexpander tool body and against the inner surface of a surroundingtubular. The tubular being acted upon by the expansion tool is thenexpanded past its point of elastic deformation. In this manner, theinner and outer diameter of the surrounding tubular is increased in thewellbore. By rotating the actuated expander tool in the wellbore andmoving the expander tool axially, a tubular can be radially expandedinto plastic deformation along a predetermined length in a wellbore.

[0007] Multiple uses for expandable tubulars are being discovered. Forexample, an intermediate string of casing can be hung off of a string ofsurface casing by expanding an upper portion of the intermediate stringinto frictional contact with the lower portion of surface casingtherearound. This allows for the hanging of a string of casing withoutthe need for a separate slip assembly as described above. Additionalapplications for the expansion of downhole tubulars exist, such as theuse of an expandable sand screen.

[0008] There are problems associated with the expansion of tubulars. Oneproblem particularly associated with the use of rotary expander tools isthe likelihood of obtaining an uneven expansion of a tubular. In thisrespect, the inner diameter of the tubular that is expanded tends toinitially assume the shape of the compliant rollers of the expandertool, including imperfections in the rollers. Moreover, as the workingstring is rotated from the surface, the expander tool may temporarilystick during expansion of a tubular, then turn quickly, and then stopagain. This spring-type action in the working string further createsimperfections in the expansion job.

[0009] Another obstacle to smooth expansion relates to the phenomenon ofpipe stretch. Those of ordinary skill in the art will understand thatraising a working string a selected distance at the surface does notnecessarily translate in the raising of a tool at the lower end of aworking string by that same selected distance. The potential for pipestretch is great during the process of expanding a tubular. Once theexpander tool is actuated at a selected depth, an expanded profile iscreated within the expanded tubular. This profile creates an immediateobstacle to the raising or lowering of the expander tool. Merely raisingthe working string a few feet from the surface will not, in manyinstances, result in the raising of the expander tool; rather, it willonly result in stretching of the working string. Applying furthertensile force in order to unstick the expander tool may cause a suddenrecoil, causing the expander tool to move uphole too quickly, leavinggaps in the tubular to be expanded.

[0010] The same problem exists in the context of pipe compression. Inthis respect, the lowering of the working string from the surface doesnot typically result in a reciprocal lowering of the expander tool atthe bottom of the hole. This problem is exacerbated by rotationalsticking, as discussed above. The overall result of these stickingproblems is that the inner diameter of the expanded tubular may not havea uniform circumference.

[0011] There is a need, therefore, for an improved apparatus forexpanding a portion of casing or other tubular within a wellbore.Further, there is a need for an apparatus which will aid in theexpansion of a tubular downhole and which avoids the potential ofpipe-stretch/pipe-compression by the working string. Correspondingly,there is a need for an expansion apparatus which will enable a rotaryexpander tool to be axially translated downhole without substantial riskof uneven tubular expansion caused by pipe-compression.

[0012] There is yet a further need for an apparatus which employs atleast one valve and at least one sized orifice for controlling the rateof translation of an expander tool during a tubular expansion operation.

SUMMARY OF THE INVENTION

[0013] The present invention provides an apparatus for expanding atubular within a wellbore. According to the present invention, anexpansion assembly is introduced into a wellbore. The expansion assemblyis lowered downhole on a working string, such as a string of drill pipe.At the same time, the expansion assembly may be releasably connected tothe lower string of casing or other tubular to be expanded. In this way,the expandable tubular is optionally lowered into the wellbore by theworking string as well.

[0014] The expansion assembly first comprises an expander tool. Theexpander tool is preferably a rotary expander tool which is lowered intothe wellbore at the lower end of a working string. The rotary expandertool defines a tubular body having recesses, with each recess containinga compliant roller. The rollers are expandable outwardly against theinner surface of a tubular to be expanded upon actuation. In one aspect,the expander tool is hydraulically actuated. In this respect, theapplication of fluid pressure from the surface, through the workingstring, and into a perforated inner bore of the expander tool generatespressure behind the rollers so as to expand them outwardly. The rollersare then placed into contact with the inner surface of the surroundingtubular to be expanded.

[0015] The expansion assembly of the present invention further comprisesa fluid chamber. The fluid chamber is loaded with an amount of cleanfluid, such as oil, before being run into the wellbore. The fluidchamber is sized to receive the body of the expander tool. In onearrangement, the fluid chamber is disposed below the body of theexpander tool and receives a lower elongated portion of the expandertool body. In this arrangement, the fluid chamber defines an outer wall,an inner wall, and a bottom wall, and receives the lower body portion ofthe expander tool. Seals are provided within the fluid chamber and/orcircumferentially around the elongated body portion of the expander toolto enable the body of the expander tool to be sealingly received withinthe inner and outer walls of the fluid chamber.

[0016] In operation, the expansion assembly of the present invention islowered into the wellbore along with the tubular to be expanded. Theexpander tool is actuated by the injection of fluid under pressure intothe drill string. As the rollers are forced outwardly against thetubular to be expanded, the drill string is rotated. This, in turn,rotates the rotary expander tool and provides for initial radialexpansion of the surrounding tubular. Thereafter, the drill string isslowly lowered further into the wellbore, causing the body of theexpander tool to be further inserted into the fluid chamber. As the bodyof the expander tool travels into the fluid chamber, it encountersresistance from the fluid loaded therein. The fluid serves as aresistant force to sudden downward movement of the drill string, therebypreventing any rapid springing of the pipe string above it.

[0017] One or more valves is placed in the outer wall of the fluidchamber. Each of the valves defines a sized orifice which serves as athrough-opening in the outer wall. The valves include apressure-sensitive diaphragm. As additional downward force is appliedagainst the fluid in the fluid chamber, the diaphragms rupture, allowingfluid to exit the fluid chamber. At the same time, resistive pressure ismaintained within the fluid chamber due to the constricted configurationof the valves. Thus, fluid is permitted to only slowly bleed from thefluid chamber as the expander tool is lowered downhole. In this manner,rapid springing of the pipe string caused by pipe-compression is furtherresisted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] So that the manner in which the above recited features of thepresent invention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings. It is to be noted, however, that the appendeddrawings illustrate only typical embodiments of this invention and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

[0019]FIG. 1 is a cross-sectional view of a wellbore having an upperstring of casing, and a lower string of casing being lowered into theupper string of casing. In this view, the lower string of casing servesas the expandable tubular. Also depicted in FIG. 1 is an expansionapparatus of the present invention for translating an expander tool.

[0020]FIG. 2 is a cross-sectional view of the expansion apparatus of thepresent invention, taken across line 2-2 of FIG. 1.

[0021]FIG. 3 presents an exploded view of an expander tool as might betranslated by a slow-bleed expansion apparatus of the present invention.

[0022]FIG. 4 presents a portion of the expander tool of FIG. 3 incross-section, with the view taken across line 4-4 of FIG. 3.

[0023]FIG. 5 is an enlarged sectional view of a fluid chamber for anexpansion apparatus of the present invention. In this view, thesurrounding upper string of casing and formation are not shown.

[0024]FIG. 6 depicts the wellbore of FIG. 1. In this view, the expandertool has been actuated so as to begin expanding the lower string ofcasing.

[0025]FIG. 7 depicts the wellbore of FIG. 6. Here, the expander tool hasbeen lowered further so as to expand the upper portion of the lowerstring of casing along a desired length.

[0026]FIG. 8 is a partial section view of the wellbore of FIG. 7, withthe slow-bleed expansion apparatus of the present invention having beenremoved. In this view, the lower string of casing has been expanded intofrictional and sealing engagement with the surrounding upper string ofcasing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027]FIG. 1 presents a cross-sectional view of a wellbore 100 having anupper string of casing 110 and a lower string of casing 120. The lowerstring of casing 120, or liner, is being lowered into the wellbore 100co-axially with the upper string of casing 110. The lower string ofcasing 120 is positioned such that an upper portion 120U of the lowerstring of casing 120 overlaps with a lower portion 110L of the upperstring of casing 110.

[0028] In the example of FIG. 1, the lower string of casing 120 servesas an expandable tubular. The lower string of casing 120 will be hungoff of the upper string of casing 110 by expanding the upper portion120U of the lower string of casing 120 into the lower portion 110L ofthe upper string of casing 110. However, it is understood that theapparatus and method of the present invention may be utilized to expanddownhole tubulars other than strings of casing.

[0029] A sealing member 222 is preferably disposed on the outer surfaceof the lower string of casing 120. Preferably, the sealing member 222defines a matrix formed in grooves (not shown) on the outer surface ofthe lower string of casing 120U. However, other configurations arepermissible, including one or more simple rings formed circumferentiallyaround the lower string of casing 120.

[0030] The sealing member 222 is fabricated from a suitable materialbased upon the service environment that exists within the wellbore 100.Factors to be considered when selecting a suitable sealing member 222include the chemicals likely to contact the sealing member, theprolonged impact of hydrocarbon contact on the sealing member, thepresence and concentration of corrosive compounds such as hydrogensulfide or chlorine, and the pressure and temperature at which thesealing member must operate. In a preferred embodiment, the sealingmember 222 is fabricated from an elastomeric material. However,non-elastomeric materials or polymers may be employed as well, so longas they substantially prevent production fluids from passing upwardlybetween the outer surface of the lower string of casing 120 and theinner surface of the upper string of casing 110 after the expandablesection 120U of the casing 120 has been expanded.

[0031] Also positioned on the outer surface of the lower string ofcasing 120 is at least one slip member 224. The slip member 224 is usedto provide an improved grip between the expandable tubular 120U and theupper string of casing 110 when the lower string of casing 120 isexpanded. In this example, the slip member 224 defines a plurality ofcarbide buttons interspersed within the matrix of the sealing member222. However, any suitable placement of a hardened material whichprovides a gripping means for the lower string of casing 120 into theupper string of casing 110 may be used. For example, a simple pair ofrings having grip surfaces (not shown) formed thereon for engaging theinner surface of the upper string of casing 110 when the lower string ofcasing 120 is expanded would be suitable. The size, shape and hardnessof the slips 224 are selected depending upon factors well known in theart such as the hardness of the inner wall of casing 110, the weight ofthe casing string 120 being hung, and the arrangement of slips 224 used.

[0032] In order to expand the lower string of casing 120 seen in FIG. 1,the present invention provides an expansion assembly 500. The expansionassembly 500 of the present invention defines two primary components—(1)an expander tool 300; and (2) a chamber 400 which receives the expandertool 300. The two components 300 and 400 are shown together within thewellbore 100 of FIG. 1, defining an expansion assembly 500. FIG. 2 isalso provided, which shows the expansion assembly 500 of FIG. 1 incross-section, with the view being taken across line 2-2 of FIG. 1.

[0033] In FIG. 1, the expander tool 300 is shown positioned above thechamber 400. In this respect, the working string 170 will be lowered,causing the expander tool 300 to be received in the chamber 400.However, it is to be understood that the scope of the present inventionpermits the expander tool portion 300 to be positioned below the fluidchamber portion 400. In such an arrangement, the working string 170 isaxially translated towards the surface of the well, causing the expandertool 300 to be raised or otherwise pulled into the fluid chamber 400.

[0034] As noted, the expansion assembly of the present invention 500first comprises an expander tool 300. An exploded view of the expandertool 300 of FIG. 1 is seen in FIG. 3. This presents an exemplaryhydraulic expander tool 300. In this embodiment, the expander tool 300first has a body 330. The body 330 is preferably an elongated tubularmember defining a bore 305 there through. As will be discussed furtherbelow, the body 330 is elongated in order to be sealingly receivedwithin a chamber 400 there below. A connector 304 is provided at anupper end of the body 330 for connection to the working string 170. Theconnector 304 is typically of a reduced diameter (compared to theoutside diameter of the body 330 of the tool 300).

[0035] The expander tool 300 next provides an inner mandrel 310. Theinner mandrel 310 runs longitudinally through the body 330. Where theexpander tool 300 is a hydraulically actuated, the inner mandrel 310 isperforated. The perforations permit fluid to fill an annular regiondefined between the inner mandrel 310 and the outer body 330, or tootherwise act on a plurality of roller members 316. FIG. 4 presents aportion of the expander tool 300 of FIG. 3 in cross-section, with theview taken across line 4-4. A portion of the perforated tubular mandrel310 is more closely seen.

[0036] The central body 330 has a plurality of recesses 314 for holdingthe respective rollers 316. In one arrangement, each of the recesses 314has parallel sides and holds a roller 316 capable of extending radiallyfrom the perforated tubular core 305 of the tool 300. The rollers 316illustrated in FIG. 3 have generally cylindrical or barrel-shaped crosssections; however, it is to be appreciated that other roller shapes arepossible. For example, a roller 316 may have a cross sectional shapethat is conical, truncated conical, semi-spherical, multifaceted,elliptical or any other cross sectional shape suited to the expansionoperation to be conducted within the tubular 120. It is understood thatany cross-sectional shape suitable for engaging the surrounding tubularmay be employed.

[0037] In the arrangement for an expander tool 300 shown in FIG. 3, eachof the rollers 316 is supported by a shaft 318 at each end of therespective roller 316. The shaft 318, in turn, is supported by a piston312. In this manner, the rollers 316 may rotate above the respectivepistons 312 about a defined rotational axis. However, the presentinvention is not limited to the manner in which the roller members 316are mounted. Alternatively, the roller members 316 may define solidbodies that reside directly on the outer piston surface. In such anarrangement, the roller members 316 may define non-rotating members thatare integral to the piston, or they may define roller bodies thatpartially roll and partially skid on the piston 312. And stillalternatively, the roller members 316 may define one or more bearingsthat reside in one or more respective races above the piston 312.

[0038] The rollers 316 are generally parallel to the longitudinal axisof the tool 300. It is permissible, however, to skew the orientation ofthe roller members 316 at a one or two degree offset in order to aid inthe axial movement of the expander tool 300. The plurality of rollers316 are radially offset at mutual circumferential separations around thecentral body 330. In the arrangement shown in FIG. 3, two rows of threerollers 316 are employed. However, additional rows may be incorporatedinto the body 330, or only one may be utilized. Various numbers ofroller members 316 may be employed.

[0039] As shown in FIG. 3, the pistons 312 are radially slidable, onepiston 312 being slidably sealed within each radially provided recess314. The back side of each piston 312 is exposed to the pressure offluid within the hollow bore 305 of the inner mandrel 310. In thismanner, pressurized fluid provided from the surface of the well canactuate the pistons 312 and cause them to extend outwardly whereby therollers 316 contact the inner surface of the surrounding tubular to beexpanded, e.g., tubular 120U.

[0040] The expander tool 300 is preferably designed for use at or nearthe end of a working string 170. In order to actuate the expander tool300 shown in FIG. 3, fluid is injected into the working string 170.Fluid under pressure then travels downhole through the working stringand into the perforated tubular bore 305 of the tool 300. From there,fluid contacts the backs of the pistons 312. As hydraulic pressure isincreased, fluid forces the pistons 312 from their respective recesses314. This, in turn, causes the rollers 316 to make contact with theinner surface of the liner 120U. Fluid finally exits the expander tool300 at the base of the mandrel 310. The circulation of fluids to andwithin the expander tool 300 is preferably regulated so that the contactbetween and the force applied to the inner wall of liner 120U iscontrolled. In this respect, fluid passing from the mandrel 310encounters a sized orifice (not shown) at the base of or below the tool500. The pressurized fluid causes the piston assembly 312 to extendradially outward so as to place the rollers 316 into contact with theinner surface of the lower string of casing 120U. With a predeterminedamount of fluid pressure acting on the piston surface 312, the lowerstring of casing 120U is expanded past its elastic limits.

[0041] Below the expander tool 300 is a chamber 400. The chamber of FIG.1 is seen more fully in the enlarged cross-sectional view of FIG. 5. Ascan be seen, the chamber 400 is comprised of an outer wall 450 and aninner wall 430. A connecting surface 460 is also shown. The outer wall450, the inner wall 430, and the connecting surface 460 define a chamber400 for containing a resistive medium. Preferably, the resistive mediumis a viscous fluid such as a clean oil, but may be any liquid material.The oil is loaded into the chamber 400 before the chamber 400 is runinto the wellbore 100. In this arrangement, the chamber 400 defines afluid chamber.

[0042] The fluid chamber 400 is sized and configured to receive theelongated tubular body 330 of the expander tool 300. A portion of thebody 330 can be seen in FIG. 5. In this view, the body 330 remains onlypartially inserted into the chamber 400, as the expander tool 300 hasnot yet been fully lowered into fluid chamber 400. Two seal rings 320and 340 are disposed around the body 330. Seal ring 320 defines an innerseal ring, and is disposed circumferentially internal to the body 330,while seal ring 340 defines an outer seal ring, and is disposedcircumferentially external to the body 330. The seal rings 320 and 340enable the body 330 to be sealingly received within the fluid chamber400 as the expander tool 300 is lowered during expansion operations.

[0043] An additional seal 355 is optionally provided between the mandrel310 and the inner wall 430. In one aspect, the seal 355 is attachedcircumferentially to the inner surface of the inner wall 430. Theoptional seal 355 is also seen in FIG. 5.

[0044] In operation, the expansion apparatus 500 of the presentinvention is run into the wellbore 100 on the lower end of a workingstring 170. In order to accomplish the expansion operation in a singletrip, the working string 170 also is temporarily connected to the lowerstring of casing 120. In this manner, the lower string of casing 120 canbe introduced into the wellbore 100 at the same time as the expandertool 300. In FIG. 1, a collet 160 is presented as the releasableconnection. The collet 160 is shown near the end of the working string170. The collet 160 is landed into a radial profile 165 within the lowerstring of casing 120 so as to support the lower string of casing 120.The collet 160 is mechanically or pneumatically actuated as is known inthe art, and supports the lower string of casing 120 until such time asthe lower string of casing 120 has been expandably set by actuation ofthe expander tool 300.

[0045] When expansion of the surrounding tubular 120U is desired, therollers 316 of the expander tool 300 are actuated as disclosed above. Atabout the same time, the rotary expander tool 300 is rotated within theexpandable tubular 120. It is contemplated in FIG. 1 that rotation ofthe expander tool 300 is accomplished by rotating the working string,i.e., drill pipe 170, from the surface. However, rotation may also beachieved by activation of a downhole hydraulic or electric rotary motor,such as a mud motor (not shown).

[0046] Once the initial section of expandable tubular 120U is expanded,the expander tool 300 is translated. In the arrangement depicted in FIG.1, the expander tool 300 is moved downwardly by slacking off the weightof the drill string 170 from the surface. This has the effect oflowering the expander tool 300 within the wellbore 100 so as to expand adesired length of tubular 120U. As the expander tool 300 is lowered, thebody 330 of the tool 300 is received within the fluid chamber 400. Theresistant medium within the chamber 400 resists entry of the body 330into the chamber 400. However, as additional weight is slacked off ofthe drill string 170 by the operator, the body 330 is urged furtherdownward.

[0047] In accordance with the present invention, at least one valvemember 480 is disposed proximate to the bottom connecting surface 460 ofthe inner and outer walls 430, 450. In the enlarged view of FIG. 5, apair of valves 480 is depicted in the connecting surface 460 of theouter wall 450. The valves 480 define through-openings havingpressure-sensitive diaphragms 485 designed to be penetrated at a givenelevated pressure within the fluid chamber 400. Preferably, the valves480 include a one-way internal member (not shown) for permitting fluidto flow from the fluid chamber 400 at a designated elevated pressure,but prohibiting wellbore fluid from flowing into the chamber 400. Thus,when pressure reaches a certain anticipated level caused by theadvancement of the expander tool body 330 into the fluid chamber 400,the valves 480 open, permitting fluid to be released.

[0048] As a further feature of the present invention, the valves 480 arespecially sized to restrict the rapid release of fluid from the fluidchamber 400. In this respect, the valves 480 are sized so that oil isreleased slowly, thereby prohibiting a rapid drop of the expander toolbody 330 into the fluid chamber 400. This, in turn, protects against anydownward pipe spring caused by pipe compression and release. Thus, a“slow-bleed” expansion apparatus is provided.

[0049] As the body 330 of the expander tool 300 continues to advanceinto the chamber 400, fluid will continue to be pushed through the atleast one valve 480. The operator may discontinue axial translation ofthe expander tool 300 before the body 330 of the expander tool 300reaches the connecting surface 460. Alternatively, the operator may push(or pull) the body 330 to the end of the chamber 400. In this approach,the length of the chamber 400 defines the length of the surroundingtubular 120 that gets expanded.

[0050] It should be noted that the slow-bleed expansion apparatus 500 ofthe present invention permits of other arrangements and embodiments. Forexample, other media besides oil may be utilized, although it ispreferred that the media be viscous. The medium may even be in a gaseousphase rather than a liquid phase. Further, a plurality of valvesdesigned to be opened at ever-increasing pressures may be employed. Inthis arrangement, a first valve would open at a first designatedpressure, while a second valve would later open at a second higherdesignated pressure. Further, the size of the through-opening attendantto the second valve may be smaller or larger than the size of the firstthrough-opening, subject to design consideration. Yet an alternatearrangement for a slow-bleed apparatus employs a subsea downhole motioncompensator system. Such a system is currently used to eliminate theeffect of rig heave during offshore operations, such as from a floatingvessel. For example, the subsea downhole motion compensator allows theoperator to control weight-on-bit during sensitive milling operations.Finally, the fluid chamber may define a single, cylindrical receptaclefor entirely receiving the body of the expander tool. The cylindricalreceptacle would have the resistive medium therein.

[0051] It is also understood that other arrangements which do not employa fluid medium may be used. For example, the resistive medium can be apowerful spring (not shown). In this arrangement, the spring is disposedwithin the chamber 400 for providing resistance against thedownward-moving expander tool body 330. In such an arrangement, the useof valves is not needed.

[0052]FIG. 6 depicts the wellbore of FIG. 1. In this view, the expandertool 300 has been actuated so as to begin expanding the lower string ofcasing 120U. Expansion is accomplished radially by rotating the actuatedexpander tool 300, such as by rotating the working string 170. In suchan arrangement, a swivel 150 is placed in the working string 170 belowthe expansion apparatus 500. The swivel 150 permits the expander tool300 to rotate without rotating other tools downhole, including thecollet 160. The swivel 150 is shown schematically in FIG. 1 as aseparate downhole tool. However, it is preferred that the swivel 150simply be incorporated into the lower end of the fluid chamber 400 usinga bearing-type connection (not shown).

[0053]FIG. 7 depicts the wellbore of FIG. 6. Here, the expander tool 300has been lowered further into the fluid chamber 400 so as to expand theupper portion of the lower string of casing 120U along a desired length.As explained above, actuation of the expander tool 300 is by injectionof fluid under pressure into the working string 170. Fluid travels fromthe surface, down the working string 170, through the bore 305 of themandrel 310, and through the perforations behind the pistons 312 of theexpander tool 300.

[0054] Following expansion operations, hydraulic pressure from thesurface is relieved, allowing the pistons 312 to return to the recesses314 within the body 330 of the tool 300. The releasable connection 160with the liner 120 is also released. The expander tool 300 and the fluidchamber 400 can then be withdrawn from the wellbore 100 by pulling therun-in tubular 170. FIG. 8 is a partial section view of the wellbore ofFIG. 7, with the slow-bleed expansion apparatus 500 of the presentinvention having been removed. In this view, the lower string of casing120 has been expanded into frictional and sealing engagement with theupper string of casing 110. This, in turn, results in an effectivehanging and sealing of the lower string of casing 120 upon the upperstring of casing 110 within the wellbore 100. Thus, the apparatus 500enables a lower string of casing 120 to be hung onto an upper string ofcasing 110 by expanding the lower string 120 into the upper string 110while avoiding the problem of pipe-spring discussed above.

[0055] It can be seen in FIG. 8 that the seal member 222 and the slipmember 224 are engaged with the inner surface of the upper string ofcasing 110. Further, the annulus 135 between the lower string of casing120 and the upper string of casing 110 has been filled with cement,excepting that portion of the annulus which has been removed byexpansion of the lower string of casing 120U. This is part of aneffective well completion enabled by the apparatus 500 of the presentinvention.

[0056] As a further aid in the expansion of the lower casing string 120,a torque anchor may optionally be utilized. Those of ordinary skill inthe art may perceive that the radially outward force applied by therollers 316, when combined with rotation of the expander tool 300, mightcause some unwanted rotation of the casing 120. The torque anchor (notshown) serves to prevent rotation of the lower string of casing 120during the expansion process.

[0057] While the foregoing is directed to embodiments of the presentinvention, other and further embodiments of the invention may be devisedwithout departing from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. An apparatus for expanding a tubular in a wellbore, the apparatus being disposed on a working string, the apparatus comprising: an expander tool, the expander tool having an elongated tubular body; a chamber for receiving a portion of the elongated tubular body when the expander tool is lowered during expansion operations; and a resistive medium within the chamber for providing resistance against the body of the expander tool as the body enters the chamber.
 2. The apparatus of claim 1, wherein the chamber comprises an outer wall having a side surface; and the resistive medium is disposed within the outer wall.
 3. The apparatus of claim 2, wherein: said chamber further comprises an inner wall; said inner wall and said outer wall are connected by a connecting surface portion of said outer wall; and said resistive medium is disposed between the inner wall and the outer wall.
 4. The apparatus of claim 3, wherein said resistive medium is a fluid.
 5. The apparatus of claim 4, wherein said resistive medium is oil.
 6. The apparatus of claim 2, wherein said resistive medium is a powerful spring.
 7. The apparatus of claim 4, wherein said chamber further comprises: at least one valve disposed proximate to the connecting surface, each valve being designed to prevent fluid from entering the chamber, but to open so as to permit fluid to exit the chamber once pressure within the chamber reaches a designated level.
 8. The apparatus of claim 7, wherein the at least one valve is sized to permit the resistive fluid medium to slowly bleed from the chamber after the valve has been opened and as the body of the expander tool advances into the chamber.
 9. The apparatus of claim 8, wherein the at least one valve includes a diaphragm.
 10. The apparatus of claim 8, wherein the at least one valve defines a one-way valve.
 11. An apparatus for expanding a tubular in a wellbore, the apparatus being disposed on a working string, the apparatus comprising: an expander tool, the expander tool having an elongated tubular body; a chamber for receiving a portion of the elongated tubular body when said expander tool is lowered during expansion operations, the chamber comprising an inner wall and an outer wall; and a resistive medium disposed between the inner wall and the outer wall of the chamber for providing resistance against the body of the expander tool as the body enters the chamber.
 12. The apparatus of claim 11, wherein said resistive medium is a fluid.
 13. The apparatus of claim 12, wherein said resistive medium is oil.
 14. The apparatus of claim 11, wherein said resistive medium is a powerful spring.
 15. The apparatus of claim 13, wherein said chamber further comprises: a connecting surface connecting the inner wall and the outer wall; and at least one valve disposed proximate to the connecting surface each valve being designed to prevent fluid from entering the chamber, but to open so as to permit fluid to exit the chamber once pressure within the chamber reaches a designated level.
 16. The apparatus of claim 15, wherein the at least one valve comprises an opening that is sized to permit the resistive fluid medium to slowly bleed from the chamber after the valve has been opened and as the body of the expander tool advances into the chamber.
 17. The apparatus of claim 16, wherein the at least one valve defines at least two valves, the at least two valves being opened in response to different pressure levels in order to incrementally throttle advancement of the body into the chamber.
 18. The apparatus of claim 16, wherein the at least one valve includes a pressure-sensitive diaphragm.
 19. The apparatus of claim 11, wherein the length of the chamber defines and controls the length of tubular that gets expanded. 